AILERONS - Movable control surfaces, usually mounted in the trailing-edge of a wing adjacent to the wingtips, to control an aircraft's rolling movements.

AIRBRAKE- A drag-inducing surface which can be deployed in flight, perhaps for speed reducing or limiting, but see also spoilers.

AIRFIELD- More modern term for aerodrome, and applying more particularly to one used by military aircraft.

AIRFLOW- The movement of air about a body (aircraft) in motion.

AIRFOIL (AEROFOIL)- A structure shaped to obtain an aerodynamic reaction in the air, thus affecting the performance of the aircraft.

AIRFRAME - An aircraft's structure, without power plant and systems.

AIRPLANE (AEROPLANE) - Meaning in modern usage a heavier-than-air powered craft, as opposed to a balloon or glider.

AIRPORT - More modern term for aerodrome, and applying more particularly to one used for civil transport operations.

AIRSCREW - Now little-used word for propeller; believed to have originated to provide distinction from ship's propeller.

AIRSHIP - A powered lighter-than-air craft.

AIRSPEED - The speed of an aircraft through the air, relative to the air mass in which it is moving.

AIRSTRIP - A natural surface used for the operation of aircraft, often in an unimproved state.

ALTIMETER - An instrument, most usually an aneroid barometer, calibrated in meters and/or feet, to indicate an aircraft's height.

ALTITUDE - Height

AMPHIBIAN - An aircraft able to operate from both land and water.

ANGLE OF ATTACK - Angle at which the air-stream meets an aerofoil surface.

ANGLE OF INCIDENCE - Angle at which an airfoil surface is normally set in relation to the fore and aft axis of the airframe structure.

ANHEDRAL - Angle which the spanwise axis of an airfoil makes to the fuselage when the wing or tailplane tip is lower than its root attachment point.

APU - Auxiliary power unit. Usually small engine carried on board an aircraft to provide an independent power source for such services as electrics, hydraulics, pneumatics, ventilation, and air conditioning, both on the ground and in the air if needed.

ASI - Air speed indicator.

ASPECT RATIO - Ratio of the span to the chord of an airfoil. Hence, a high aspect ratio wing has great span and narrow chord, and vice versa.

AUTOGYRO - An aircraft with an unpowered rotary wing, which autorotates as the machine is propelled through the air by a conventional power plant. "Autogiro" is the trade name for autogyros developed by Juan de la Cierva.

AUTOMATIC PILOT (AUTOPILOT) - A gyroscopically stabilized system maintaining an aircraft in level flight at predetermined heading and altitude.

AUTOROTATION - Automatic rotation of a rotary wing due to forward, or downward, movement of an autogyro

AWACS - Airborne warning and control system; an advanced AEW aircraft, with additional facilities for deployment and control of defence, interception, and counter-strike forces.

BALLISTIC MISSILE - A weapon which, in the terminal and unpowered stage of its flight, becomes a free-falling body subject to ballistic reactions.

CANARD - Describes an aircraft which flies tail first, with its main lift surface at the aft end of its structure.

CANTILEVER - A beam, or other structure, supported at one end only, and without external bracing.

CATHEDRAL - Early word to describe anhedral, or negative dihedral.

CEILING - Normal maximum operating altitude of an aircraft.

CENTER OF GRAVITY - (CQ), the point on an aircraft's structure where the total combined weight forces act.

CENTER-SECTION - The central panel, or section, of an aircraft's wing.

CHORD - The distance measured from the leading-to trailing-edge of an airfoil.

COCKPIT - Compartment, originally open to the air, for accommodation of pilot'and crew/passengers. Nowadays used informally by laymen to describe the forward part of the cabin, especially of an airliner, which is off-limits to passengers, and properlv called flight deck.

COIN - Counter-insurgency aircraft.

COLLECTIVE PITCH CONTROL - Used to change simultaneously the pitch of all of a helicopter rotor's blades to permit ascent or descent.

CONSTANT-SPEED PROPELLER - One which governs an engine at its optimum speed, the blade pitch being increased or decreased automatically to achieve this result.

COWLING - The name of the fairing which, usually, encloses an engine.

CYCLIC PITCH CONTROL - Means of changing the pitch of a rotor's blades progressively, to provide a horizontal thrust component for flight in any horizontal direction.

DELTA WING - When viewed in plan has the shape of an isosceles triangle; the apex leads, the wing trailing-edge forming the base of the triangle.

DERATED - An engine which is restricted to a cower output below its potential maximum.

DIHEDRAL - Angle which the spanwise axis of an aerofoil makes to the fuselage when the wing or tailplane tip is higher than its root attachment point (positive dihedral).

IN-LINE ENGINE - Engine in which the cylinders are one behind another, in straight lines.

INS - Inertial navigation system, in which highly sensitive accelerometers record, via a computer, the complex accelerations of an aircraft about its three axes, thus integrating its linear displacement from the beginning of a selected course and pinpointing the aircraft's position at all times.

LEADING-EDGE - The edge of an airfoil which first meets the airstream in normal flight.

LIFT - The force generated by an airfoil section, acting at right angles to the airstream flowing past it

LORAN - A long-range radio-based navigation aid.

LOW-WING MONOPLANE - An aircraft which has its single wing mounted low on the fuselage.

MACH NUMBER - Named after the Austrian physicist Ernst Mach, a means of recording the speed of a body as a ratio of the speed of sound in the same ambient conditions. The speed of sound in dry air at 32"F (CTC) is approximately 1087ft/sec (331m/sec); 741mph (1193km/h). Hence Mach 0.8 represents eight-tenths of the speed of sound.

MAD - Magnetic anomaly detector carried, for example, by maritime reconnaissance aircraft to locate a submarine beneath the surface of the sea.

MID-WING MONOPLANE - An aircraft which has its single wing mounted in a mid-position on the fuselage.

MONOCOQUE - Structure in which the outer skin carries the primary stresses, and is free of internal bracing.

MONOPLANE - A fixed-wing aircraft with a single set of wings, i.e. one wing on each side.

NACA - National Advisory Committee for Aeronautics. Now NASA.

NAF - Naval Aircraft Factory (U.S.).

NASA - National Aeronautics and Space Administration.

NATO - North Atlantic Treaty Organization.

ORNITHOPTER - Name for a flapping-wing aircraft. Only model ornithopters have flown to date.

PARACHUTE - Collapsible device which, when deployed, will retard the rate of descent of a body falling through the air. Used originally as a safety device, has been adopted for dropping troops, supplies, equipment, etc.

PARASOL MONOPLANE - A fixed-wing aircraft which has its single wing strut-mounted above the fuselage.

PAYLOAD - The useful load of an aircraft cargo, passengers; in a military aircraft, its weapon load.

PITCH - The angle of incidence at which a propeller blade or rotor blade is set.

PORT - Left-hand side when facing forward.

PRESSURIZATION - Artificially increased pressure in an aircraft to compensate for the reduced external pressure as the aircraft gains altitude.

PROPELLER - Rotating blades of aerofoil section, engine driven, each of which reacts as an aircraft's wing, generating low-pressure in front and higher behind, thus pulling the aircraft forward.

PROTOTYPE - The first airworthy example of a new aircraft design or variant.

PUSHER PROPELLER - Inaccurate but accepted description of propeller mounted behind an engine. It acts aerodynamically as described under propeller, and is thus a tractor in action.

TRIPLANE - Fixed-wing aircraft with three sets of wings, mounted one above another.

TURBOFAN - Gas turbine engine with large diameter forward fan. Air is dueled from the tips of these fan blades and by-passed around the engine, and added to the normal jet efflux to provide high propulsive efficiency.

TURBOPROP - Gas turbine engine in which maximum energy is taken from the turbine to drive a reduction gear and conventional propeller.

TURBOSHAFT - Gas turbine engine in which maximum energy is taken from the turbine to drive a high speed shaft. It can be used to drive a helicopter's rotor or any other form of machinery.

VARIABLE-GEOMETRY WING - Wings which, fully extended, give the best low-speed performance for take-off and landing, and can be swept in flight to optimum positions for best cruising and high-speed flight performance.

VARIABLE-PITCH PROPELLER - Usually a propeller in which the blades can be set to two positions a fine-pitch setting for take-off and landing, and a coarse-pitch setting for economic cruise performance.

VEE-ENGINE - One with two banks of in-line cylinders mounted with an angular separation on a common crankcase.

WING-LOADING - The gross take-off weight of an aircraft divided by its wing area. A Boeing 747, for example, can have a maximum wing loading of 149Ib/sq ft (727.8kg/m2); a high-performance sailplane, such as the Scheibe Bergfaike, can be as low as 6.02Ib/sq ft (29.4kg/m2).

WING WARPING - Method of lateral control adopted by Wright brothers and many early builders/designers, in which a flexible wing is twisted (warped) to provide roll control as with ailerons.

YAW - Movement of an aircraft about its vertical axis, representing movement of its tail unit to port or starboard, to change the aircraft's heading.